The present invention relates generally to mechanical interface devices between humans and computers, and more particularly to mechanical devices for tracking manual manipulations and providing simulated force feedback.
Virtual reality computer systems provide users with the illusion that they are part of a xe2x80x9cvirtualxe2x80x9d environment. A virtual reality system will typically include a computer processor, such as a personal computer or workstation, specialized virtual reality software, and virtual reality I/O devices such as display screens, head mounted displays, sensor gloves, etc. As virtual reality systems become more powerful and as the number of potential applications increases, there is a growing need for specific human/computer interface devices which allow users to interface with computer simulations with tools that realistically emulate the activities being represented within the virtual simulation.
One common use for virtual reality computer systems is for training. In many fields, such as aviation and vehicle and systems operation, virtual reality systems have been used successfully to allow a user to learn from and experience a realistic xe2x80x9cvirtualxe2x80x9d environment. The appeal of using virtual reality computer systems for training relates, in part, to the ability of such systems to allow trainees the luxury of confidently operating in a highly realistic environment and making mistakes without xe2x80x9creal worldxe2x80x9d consequences. One highly applicable field for the use of virtual training system is medical operations and procedures. A virtual reality computer system can allow a doctor-trainee or other human operator or user to xe2x80x9cmanipulatexe2x80x9d a needle, scalpel or probe within a computer-simulated xe2x80x9cbodyxe2x80x9d, and thereby perform medical procedures on a virtual patient. In this instance, the I/O device which is typically a 3D pointer, stylus, or the like is used to represent a surgical instrument such as a probe or scalpel. As the xe2x80x9cprobexe2x80x9d or xe2x80x9cscalpelxe2x80x9d moves within a provided space or structure, results of such movement are updated and displayed in a body image displayed on a screen of the computer system so that the operator can gain the experience of performing such a procedure without practicing on an actual human being or a cadaver.
Other uses for virtual reality computer systems include entertainment. Sophisticated simulations and video games allow a user to experience virtual environments with high degrees of realism, thus providing highly interactive and immersive experiences for the user.
For virtual reality systems to provide a realistic (and therefore effective) experience for the user, sensory feedback and manual interaction should be as natural and complete as possible. One essential sensory component for many experiences is the xe2x80x9chapticxe2x80x9d and tactile senses. The haptic sense is typically related to the sense of touch not associated with tactility, such as the forces sensed when pushing or pulling on an object. The tactile sense is more concerned with the texture and feel of a surface or object.
Medical operations and procedures using such medical instruments as catheters, laparoscopes, and needles have, a distinct haptic component that is essential to performing the procedures correctly and effectively. For example, epidural anesthesia is a highly delicate procedure performed by anesthesiologists in operations. In this procedure, a four inch needle is directed between two vertebrae in the lower back of the patient, through extremely dense tissue, and into an epidural space no larger than {fraction (1/20)}th of an inch. Overshooting the epidural space may result in a xe2x80x9cwet tapxe2x80x9d puncturing the dura mater, resulting in severe spinal headaches for the patient, or, in extreme cases, damage to the spinal cord.
This insertion is accomplished only through the sense of feel, i.e., the haptic sense. The vast majority of physicians use a technique known as the xe2x80x9closs of resistancexe2x80x9d method. The fluid in the syringe (typically a saline solution or simply air) is retarded by the dense ligaments as the needle is inserted. The administrator will feel a slight xe2x80x9cpopxe2x80x9d as the ligamentum flavum (the layer positioned just before the epidural space) is punctured, due to a slight pressure drop from entering the epidural space. The contents of the syringe then flow freely into the epidural space, gently expanding the separation of the two tissue layers. A catheter can subsequently be fed through the center of the epidural needle so that an anesthetic can be metered through an IV.
Currently there is no practical and effective training tool to assist trainees in developing proficiency in the administration of epidural anesthesia and like medical procedures. Mannequins and cadavers often do not meet many of the needs of trainees for such precise manipulations. Thus, a highly accurate virtual reality system would be ideal for this and other types of applications, especially a xe2x80x9chigh bandwidthxe2x80x9d interface system, which is an interface that accurately responds to electronic signals having fast changes and a broad range of frequencies as well as mechanically transmitting such signals accurately to a user.
There are number of devices that are commercially available for interfacing a human with a computer for virtual reality simulations. Some of these devices provide xe2x80x9cforce feedbackxe2x80x9d to a user, i.e., the user interface device outputs forces through the use of computer-controlled actuators and sensors to allow the user to experience haptic sensations. However, none of these devices is tailored for such precise operations as epidural anesthesia. For example, in typical multi-degree of freedom apparatuses that include force feedback, there are several disadvantages. Since actuators which supply realistic force feedback tend to be large and heavy, they often provide inertial constraints. There is also the problem of coupled actuators. In a typical force feedback device, a serial chain of links and actuators is implemented to achieve multiple degrees of freedom for a desired object positioned at the end of, the chain, i.e., each actuator is coupled to the previous actuator. The user who manipulates the object must carry the inertia of all of the subsequent actuators and links except for the first actuator in the chain, which is grounded. While it is possible to ground all of the actuators in a serial chain by using a complex transmission of cables or belts, the end result is a low stiffness, high friction, high damping transmission which corrupts the bandwidth of the system, providing the user with an unresponsive, and inaccurate interface. These types of interfaces also introduce tactile xe2x80x9cnoisexe2x80x9d to the user through friction and compliance in signal transmission and limit the degree of sensitivity conveyed to the user through the actuators of the device.
Other existing devices provide force feedback to a user through the use of a glove or xe2x80x9cexoskeletonxe2x80x9d which is worn over the user""s appendages, such as fingers, arms, or body. However, these systems are not easily applicable to simulation environments such as those needed for medical procedures or simulations of vehicles and the like, since the forces applied to the user are with reference to the body of the user, not to a manipulated instrument or control, and the absolute location of the user""s appendages or a manipulated instrument are not easily calculated. Furthermore, these devices tend to be complex mechanisms in which many actuators must be used to provide force feedback to the user.
In addition, existing force feedback devices are typically bulky and require that at least a portion of the force feedback mechanism extend into the workspace of the manipulated medical instrument. For example, in simulated medical procedures, a portion of the mechanism typically extends past the point where the skin surface of the virtual patient is to be simulated and into the workspace of the manipulated instrument. This can cause natural actions during the medical procedure, such as placing one""s free hand on the skin surface when inserting a needle, to be strained, awkward, or impossible and thus reduces the realism of the simulation. In addition, the mechanism intrudes into the workspace of the instrument, reducing the workspace of the instrument and the effectiveness and realism of many force feedback simulations and video games. Furthermore, this undesired extension into the workspace often does not allow the force feedback mechanism to be easily housed in a protective casing and concealed from the user.
Furthermore, prior force feedback devices often employ low fidelity actuation transmission systems, such as gear drives. For higher fidelity, cable drive systems may be used. However, these systems require that a drive capstan be wrapped several times with a cable and that the cable be accurately tensioned, resulting in considerable assembly time of the force feedback device. There is also energy loss associated with the cable deflection as the capstan turns.
Therefore, a high fidelity human/computer interface tool which can provide force feedback in a constrained space to a manipulated object remote from the mechanism, and which can provide high bandwidth, accurate forces, is desirable for certain applications.
The present invention provides a mechanical interface apparatus and method which can provide highly realistic motion and force feedback to a user of the apparatus. The preferred apparatus includes a gimbal mechanism which provides degrees of freedom to a user manipulatable object about a remote pivot point such that the gimbal mechanism is entirely within a single hemisphere of a spherical workspace of the user object. In addition, a band drive mechanism provides mechanical advantage in applying force feedback to the user, smooth motion, and reduction of friction, compliance, and backlash of the system. The present invention is particularly well suited to simulations of medical procedures using specialized tools, as well as simulations of other activities, video games, etc.
Specifically, a mechanism of the present invention includes a gimbal mechanism for providing motion in two degrees of freedom. The gimal mechanism includes multiple members that are pivotably coupled to each other to provide two revolute degrees of freedom about a pivot point located remotely from the members. The pivot point is located at about an intersection of the axes of rotation of the members. A linear axis member is coupled to at least one of the members, extends through the pivot point and is movable in the two revolute degrees of freedom. The linear axis member preferably is or includes a user manipulatable object.
In a preferred embodiment, the gimbal mechanism includes five members forming a closed loop chain such that each of the five members is pivotably coupled to two other members of said five members. The multiple members of the gimbal mechanism are positioned exclusively within a hemisphere of a sphere defined by the workspace provided by the gimbal mechanism, i.e., on one side of a plane intersecting the remote pivot point, where the pivot point is at a center of the sphere. Preferably, the user manipulatable object is independently translatable with respect to the gimbal mechanism along a linear axis in a third degree of freedom through the pivot point, and at least a portion of the user object is positioned on the opposite side of the pivot point to the gimbal mechanism.
The gimbal mechanism interfaces the motion of the linear axis member in two degrees of freedom with a computer system. Transducers, including actuators and sensors, are coupled between members of the gimbal mechanism for an associated degree of freedom and are coupled to the computer system. The actuators provide a force on the linear axis member and the sensors sense the position of the linear axis member in the three degrees of freedom. Preferred user manipulatable objects include at least a portion of a medical instrument, such as a needle having a shaft and a syringe. A plunger actuator can be coupled to the needle for selectively providing a pressure to a plunger of the syringe and simulating ejected of a fluid through the needle. Alternatively, a spherical object or other type of object can be provided with the pivot point at about the object""s center.
In another aspect of the present invention, the interface apparatus includes a band drive mechanism for transmitting forces from actuators to the user object and transmitting motion of the object to sensors. The band drive mechanism includes a capstan coupled to a rotating shaft of an actuator of the apparatus and to a member of the apparatus by a flat band. Force is applied to the member in at least one degree of freedom via the flat band when the shaft of the actuator is rotated. Preferably, a band drive mechanism is used for both rotary and linear degrees of freedom of the interface apparatus and transmits forces and motion with substantially no backlash. The flat band preferably includes two separate bands coupled between the capstan and the mechanism member.
In yet another aspect of the present invention, the interface apparatus is used in a computer simulation, such as a simulation of a medical procedure where the user-manipulable object is a medical instrument. The computer system determines the position of the user manipulatable object in at least one degree of freedom from sensors. A physical property profile is then selected. The profile includes a number of predetermined values, such as material stiffness, density, and texture, and the selection of the particular values of the profile is based on a position of the user object. Finally, a force on the user object is output based on a value in the selected profile using actuators coupled to the interface apparatus. Preferably, forces are also output from the actuators to compensate for the gravitational force resulting from the weight of the actuators and to allow the user object to be manipulated free from gravitational force. The profile is selected from multiple available profiles and is also dependent on a direction and trajectory of movement of the user object. In a described embodiment, the medical simulation is an epidural anesthesia simulation, and the user object includes a needle having a syringe. For example, one of the selected profiles can be to provide forces simulating the needle encountering a bone within tissue.
The interface apparatus of the present invention provides a unique gimbal mechanism having a remote pivot point that allows a user manipulatable object to be positioned on one side of the pivot point and the gimbal mechanism entirely on the other side of the pivot point. This provides a greater workspace for the user object and allows the mechanism to be protected and concealed. In other embodiments, the remote pivot point allows the user object to be rotated about the center of the object while advantageously allowing the user to completely grasp the object. Furthermore, the present invention includes easy-to-assemble band drive mechanisms that provide very low friction and backlash and high bandwidth forces to the user object, and are thus quite suitable for high precision simulations such as medical procedures. The structure of the apparatus permits transducers to be positioned such that their inertial contribution to the system is very low, thus enhancing the haptic response of the apparatus even further. Finally, a simulation process allows for realistic simulation of precise procedures such as epidural anesthesia. These advantages allow a computer system to have, more complete and realistic control over force feedback sensations experienced by a user of the apparatus.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawing.